Figure 5.

Phylogenetic tree of NifH based on the translated amino acid sequence, constructed by the neighbor-joining method in MEGA 6. The scale bar indicates the number of sequence substitution per sites. Sequences retrieved in this study fell into 22 groups (NS1-NS22) and are shown in bold. Table S1 gives all sequences in groups NS1–NS22. Groups that contain sequences from both genomic DNA and cDNA are marked by a solid circle. Asterisks indicate groups that contain sequences from the water column. nifH sequences that have been reported previously as potential contaminants in RT-PCR reagents are marked by a solid triangle.